1. Field of the Invention
This invention relates generally to motorized riding trowels for finishing concrete surfaces of the type classified in United States Patent Class 404, Subclass 112. More particularly, our invention relates to twin-rotor riding trowels comprising joystick-activated, fluid operated systems for controlling steering.
2. Description of the Prior Art
It is well established in the art that freshly placed concrete must be appropriately finished to achieve the desired smoothness and flatness. Motorized riding trowels are particularly effective for finishing concrete. They can finish large surface areas of wet concrete more efficiently than older "walk behind" trowels. Significant savings are experienced by the contractor using such equipment, as time constraints and labor expenses are reduced.
Typical motorized riding trowels employ multiple, downwardly projecting rotors that are gimbaled to the frame for pivoting. The rotors contact the concrete surface for finishing concrete and support the weight of the trowel. Typically, each rotor comprises a plurality of radially spaced apart finishing blades that revolve in frictional contact with the concrete surface. The blades may be coupled to circular finishing pans for treating green concrete. The rotors and their revolving blades are responsible for steering and propulsion. When the rotors are tilted, the differential forces generated upon the concrete by the revolving rotor blades generate steering and propulsion moments.
As freshly poured concrete "sets", it soon becomes hard enough to support the weight of motorized trowels. Preferably, the finishing process starts with panning while the concrete is still "green", within one to several hours after pouring depending upon the concrete mixture involved. The advent of more stringent concrete surface finish specifications using "F" numbers to specify flatness (ff) and levelness (fl), dictates the use of pans on a widespread basis. Both "super-flat" and "super-smooth" floors can be achieved by panning with motorized trowels.
Pan finishing is normally followed by medium speed blade finishing, after the pans are removed from the rotors. A developing technique is the use of "combo blades" during the intermediate "fuzz stage" as the concrete continues to harden. So-called "combo-blades" are a compromise between pans and normal finishing blades. They present more surface are to the concrete than normal finishing blades, and attack at a less acute angle. The rotors are preferably turned between 100 to 135 RPM at this time. Finishing blades are then used, and they are rotated between 120 to 150 RPM. Finally, the pitch of the blades is changed to a relatively high contact angle, and burnishing begins. This final trowel finishing stage uses rotor speeds of between 135 and 165 RPM.
Motorized riding trowels are ideal for finishing large areas of plastic concrete quickly and efficiently, and a variety of self propelled riding trowels are known in the art.
Holz, in U.S. Pat. No. 4,046,484 shows a pioneer, twin rotor, self-propelled riding trowel wherein the rotors, gimbaled to the frame, are appropriately tilted to generate steering forces. U.S. Pat. No. 3,936,212, also issued to Holz, shows a three rotor riding trowel powered by a single motor. Although the design depicted in the latter two Holz patents were pioneers in the riding trowel arts, the devices were relatively difficult to steer and control.
Prior U.S. Pat. No. 5,108,220 owned by Allen Engineering Corporation, the same assignee as in this case, relates to an improved, fast steering system for riding trowels. Its steering system enhances riding trowel maneuverability and control. The latter fast steering riding trowel is also the subject of U.S. Des. Pat. No. 323,510 owned by Allen Engineering Corporation. U.S. Pat. No. 5,613,801, issued Mar. 25, 1997 to Allen Engineering Corporation discloses a power-riding trowel equipped with separate motors for each rotor. These designs employ upwardly projecting, manually deflected levers for steering and control.
Allen Engineering Corporation U.S. Pat. No. 5,480,258 discloses a multiple engine riding trowel. The twin rotor design depicted therein associates a separate engine with each rotor. As the engines are disposed directly over each revolving rotor assembly, horsepower is more efficiently transferred to the revolving blades. Besides resulting in a faster and more efficient trowel, the design is easier to steer. Again, manually activated steering linkages are used.
Allen Engineering Corporation U.S. Pat. No. 5,685,667 discloses a twin engine riding trowel using "contra rotation." Many trowel users prefer the steering characteristics that result when the trowel rotors are forced to rotate in a direction opposite from that normally expected in the art.
Modern large, high power riding trowels are noted for their speed, horsepower, and efficiency. To be effective they must be highly maneuverable and easy to operate. The steering must be fast and responsive. The trowel must be capable of operation over a variety of engine speeds. Further, all of the foregoing characteristics must be preserved whether the trowel is finishing with pans, combo-blades, or normal finishing blades of a variety of sizes. Generally speaking, the more powerful the trowel, the faster finishing operations can be completed. However, with more power it becomes harder to control and properly steer the machine. Crisp, responsive handling is important to optimize the efficiency of the troweling process, and to preserve operator safety and comfort.
The rotors in many of the previously discussed patents are tilted with manually operated levers that project upwardly from the machine frame. The operator manually controls the levers to deflect linkages below the trowel frame that tilt the rotors. Where separate engines are used with each rotor assembly, the added weight requires additional physical effort to tilt the rotors for steering, or to vary blade pitch. It is clear that to meet all of the demands placed upon the modern riding trowel, a powered steering system must be perfected.
Hence we have designed a twin rotor riding trowel with an optimized steering control system. The titling cylinders are controlled proportionally, and direct hydraulic-joystick systems are employed. Our hydraulic steering system is "backwards compatible" dual-rotor trowels. Our system can be adjusted to readily adapt itself for use with finishing pans, combo blades, or normal blades. Further, it readily adapts itself to drivers of different weight. Handling characteristics can be somewhat customized to approximate the desired "feel" of the individual driver by our new "select steering" system.